While not limited thereto, the present invention is particularly adapted for use with electronic balancing apparatus for rotating bodies and the like. Vibration analyzing apparatus of this type must be capable of measuring the magnitude, frequency and phase of vibration caused by a rotating body. Furthermore, when there are two or more sources of vibration in a piece of equipment to be balanced, as is quite often the case, the analyzing equipment must be capable of separating a particular frequency associated with a single vibrating part from all other frequencies in order to effect a balancing or corrective operation.
In order to sense mechanical vibrations, the analyzing apparatus utilizes a vibration responding transducer which transforms the vibrations into an electrical signal having a frequency equal to that of the vibrations, an amplitude proportional to the magnitude of the vibrations, and a phase displacement relative to a reference signal which is related to the location of a point of unbalance on a rotating body. The resulting vibration signal is then applied to apparatus including an amplitude meter for indicating the level (amplitude) of the vibrations, a frequency meter for indicating the signal frequency, a filter to separate selected frequencies of vibration for individual measurement, and a phase determining means such as a phase indicator or strobe light.
Generally in the past, an operator assigned the task of carrying out an on-site vibration analysis of an industrial machine has been provided one or more portable devices constituting the above apparatus. Upon connecting the apparatus with the vibration responding transducer, a knob or dial having indicia associated therewith corresponding with a predetermined range of frequencies was manipulated to alter the frequency response of the apparatus to detect vibrational frequencies which corresponded with relatively high vibrational amplitudes, such higher amplitude generally being associated with a frequency representing a potential machine defect. Detection of such a peak amplitude generally was achieved by observing the noted amplitude meter which was present as a conventional analog-type having a dial and associated scale. A conventional, analog-type frequency meter with associated dial and scale then was read to determine, as closely as possible, the frequency at which that peak vibrational amplitude occurred. The experience of the industry has shown that such frequencies represent a highly important criterion for analyzing actual or impending machine defects. Accordingly, the accuracy of such frequency reading and its proper correlation to a genuine amplitude has been considered important to proper machine analysis.
In seeking to find significant peak amplitudes utilizing the analyzing apparatus, the operator generally turns to two approaches. If a pre-existing awareness of critical frequency regions is available, the operator turns the frequency selection knob directly to those regions and manipulates or "rocks" it while simultaneously observing the amplitude readout. Alternately, where no such preconceived awareness is present, the operator "scans" across the spectrum of frequencies available from the transducer derived vibrational signal while recording frequencies corresponding with all observed peak amplitude vibration signals.
The analyzing apparatus and associated techniques of use as thus described, while having been found to be quite effective, are not adequately precise to permit very high readout accuracies for deriving correspondingly more predictive defect identification. For example, the analog meters utilized for frequency and amplitude readout are inherently limited to precisions of about 1 or 2%. For many vibration analysis applications, such accuracies are inadequate. While digital readout devices are available in the market place having much higher capabilities for precision, e.g. better than 0.01%, their digital readout response or "update rate" is rapid to an extent wherein operators become confused as they manually manipulate the frequency tuning knob, the apparatus then having the attribute of being oversensitive to the extent of being impractical.
Conventional filters utilized in carrying out the above-described frequency spectrum scanning are tuned by manually varying the resistance, capacitance or inductance of selected filter elements. Such tuning approaches have been found to exhibit operational limitations. For example, varying a resistance parameter by means of a potentiometer poses frequency range or band limitations. To achieve adequate frequency scanning range, therefore, ganged potentiometer components in association with multi-range selection switching typically is resorted to. Thus, to carry out full vibrational frequency scanning, the operator has been called upon to perform a variety of manipulative tasks, a situation to be avoided in developing more effective tools for vibration analysis.